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Resistor values on TS lines for BQ24190

Kuenrg
Intellectual 480 points
Other Parts Discussed in Thread: BQ24190, BQ24193

Hi, 

  I would just like to clarify the values shown on pages 28 & 29 of the BQ24190 datasheet.

Is the datasheet saying that for bq24190/91/92 devices we should use:

RT1 = 5.52 kΩ
RT2 = 31.23 kΩ

and for BQ24193 we should use:

RT1 = 2.27 kΩ
RT2 = 6.86 kΩ

What if we use the second set of values on a bq24190?  How will the charging behave.

(Background, we are seeing unpredictable charging behavior on our boards and I am trying to find the source of it.)

Thanks in advance,

Kurtis

  • 0
    TI__Genius 13700 points

    Hello Kurtis,

    Both the BQ24190 and the BQ24193 use the same source to bias the TS network which is the internal REG LDO.

    Since the bias voltage is the same and the recommended NTC value of 10Kohm is the same for both devices if the size of these resistors change the influence that variation in the NTC resistance will be influenced.

    In the case of the bq24190/91/92 the resistor divider of:

    RT1 = 5.52 kΩ
    RT2 = 31.23 kΩ

    Has a 10kohm NTC in parallel with RT2 making the setting a peak division of less than 2/3.

    The BQ24193 case has an entirely different set of resistors since it is comparing against a different set of thresholds.

    RT1 = 2.27 kΩ
    RT2 = 6.86 kΩ

    Please follow the design calculations provided in the datasheet for each specific device since they are recommended to fit the comparator thresholds for the temperature control scheme of each device.

     

    What is the erratic operation that you are seeing? Are you seeing any of the following cases that has lead you to believe it is TS related.

    -Charge current limited to 1/2 fast charge current during the constant current portion of the charge.

    -Charge voltage limited to 4.1V

    -Device not charging even when charging is enabled.

  • 0 in reply to Ryan May
    Intellectual 480 points

    Hi Ryan,

      Thanks for the quick reply!  I'm in the process of trying to characterize the erratic charging behaviour.  At this point I can say that some boards charge while others do not.  It also seems that boards that were charging normally sometimes stop (I'm trying to see if this follows the battery or the board.) 

      I think we are seeing some of the behaviour you list; specifically device not charging when charging is enabled, I'll do some more investigation.  (Unfortunately I don't actually have any testable boards with me at the moment so I need to get feedback from teammates.) 

    - Kurt

  • 0 in reply to Kuenrg
    TI__Genius 13700 points

    Hello Kurt,

    Let me know when you have a chance to run through some tests on your boards.

    Are the same boards consistently failing to charge or is it intermittent?

    Could you post a schematic of your system?

    Do you have any information about your battery that you could post?